Critical role of C/SiO₂ composite coating in enhancing the mechanical and antioxidation properties of 3D needled carbon fibers

Herein, a hydrothermal carbonization coating/SiO₂ (HTCC/SiO₂) composite coating on 3D needled carbon fibers (Cf/HTCC-SiO₂) was successfully designed and constructed through a combined hydrothermal carbonization and sol-gel process for the first time. The results revealed that the microstructure and morphology of HTCC and SiO₂ coatings strongly depended on the key process parameters in the synthetic process. The optimal conditions for fabrication of Cf/HTCC-SiO₂ were achieved as following: the hydrothermal temperature was 180 °C and holding time was 2 h; the TEOS mass fraction was 30 wt%, the distilled water/ethanol molar ratio was 6:1 and sol-gel time was 2 h, respectively. The relatively continuous and uniform HTCC/SiO₂ composite coating with a single thickness about 350 and 300 nm effectively improved the mechanical and anti-oxidation of 3D needled Cf. Compared with the uncoated 3D needled Cf, the compressive strength was increased about 336% and the rapid oxidation temperature was improved about 100 °C after the incorporation of HTCC/SiO₂ composite coating.